Articles composed of materials having refractory characteristics, such as hardness and resistance to erosion may be used as cutting inserts in the fields of metal machining, such as boring, drilling and the like. Representative materials are described in U.S. Pat. No. 2,938,807 to Anderson.
Such materials must be tough, wear-resistant, capable of high temperature operation, and must be shock resistant to prevent chipping or cracking. In operation, a cutting insert is placed in a tool holder, or a milling cutter body, and clamped tightly. Since the clamp or wedge is hardened, the clamped surfaces of the cutting insert must be parallel and well finished. Any stress concentration due to non-uniform surfaces may cause cracking of the insert during machining operations.
U.S. Pat. No. 4,219,339 to Wilson discloses a diamond insert onto which two rigid materials are brazed to cover both surfaces of the insert. The rigid material brazed on the top of the diamond insert does not provide any shock aborbing function to prevent chipping of the diamond during a cutting operation, however. Further, in order to braze the rigid metal to the diamond material, the surface of the diamond must be ground to perfect parallelism, requiring an inordinate amount of time and expense. Still further, the cutting insert disclosed in U.S. Pat. No. 4,219,339 is not indexable.
Another technique for facilitating the clamping of a cutting insert into a cutting tool is provided in commercially available diamond COMPAX.RTM., produced by the assignee of the present invention. A polycrystalline diamond body is liquid phase sintered onto a carbide substrate of high cobalt content to produce a blank. The blank is then finished and brazed onto a pocket in a tungsten carbide insert of standard thickness and parallelism. Only one pocket is provided on the insert and is therefore not indexable. Further, the polycrystalline diamond material is made by a high temperature high pressure process which is expensive and time consuming.
A technique for producing a polycrystalline composite for use in a cutting insert is described in co-pending U.S. patent application Ser. Nos. 167,019 and 167,196, both filed July 9, 1980, both by Dr. John M. Ohno, and assigned to the assignee of the present invention, the entire disclosures of which are hereby incorporated by reference. In these applications, a straightforward technique (hereinafter referred to as "press and treat technique") for forming high quality cutting inserts having cutting surfaces at a plurality of locations, yet which readily lends itself to mass production is disclosed. Very briefly, the press and treat technique involves the preparation of a first dispersion of super-hard crystals such as diamond or cubic boron nitride crystals in carbon black, and a second dispersion of carbon black, carbon fiber and filler material. The two dispersions are individually mixed with a temporary binder such as paraffin to lend a sufficient green strength to the two dispersions upon cold compaction thereof. After compacting the two dispersions together in a configuration which provides a plurality of cutting edges on the insert, the compact is vacuum heated in the presence of silicon to burn off the paraffin and to allow the silicon to infiltrate both dispersions. Upon further heating, and without the need for the constant application of any type of pressure to the insert, the silicon reacts with the carbon black to form a matrix of .beta.-silicon carbide and silicon which bonds both dispersions both internally and to each other.
In co-pending U.S. patent application Ser. No. 226,603, filed Jan. 21, 1981, by Dr. John M. Ohno, and assigned to the assignee of the present invention, the entire disclosure of which is hereby incorporated by reference, an indexable, sandwiched multi-layer composite cutting insert is described and is shown herein in FIG. 1. The reaction sintered layers 10 and 12 produced by the above-mentioned press and treat technique are sandwiched by an aluminum or copper metal sheet 14 bonded to the top of crystal layer 10 and a metal carbide substrate 16 bonded to the bottom of core layer 12. The insert produced in accordance with Ser. No. 226,603, although having substantially perfect parallelism, produces an insert which is thicker than standard, and thus requires special mounting devices on the tool holder.
Another co-pending U.S. patent application Ser. No. 331,379, filed Dec. 16, 1981, by Dr. John M. Ohno, filed concurrently herewith and assigned to the assignee of the present invention, the entire disclosure of which is incorporated by reference, describes a multi-layer composite similar to that produced in accordance with Ser. No. 226,603, except for the particular configuration of the reaction sintered layers, carbide substrate and metallic top plate.
Still a further technique of simplifying the task of providing highly parallel surfaces for the cutting insert is disclosed in co-pending U.S. patent application Ser. No. 331,365, filed Dec. 16, 1981, by Dr. John M. Ohno, filed concurrently herewith and assigned to the assignee of the present invention, the entire disclosure of which is also incorporated by reference, wherein a polygonal cutting insert having a plurality of super-hard crystal cutting surfaces disposed exclusively at the corners of the polygonal insert, is disclosed. The super-hard crystal portions at the corners of the insert are elevated relative to the central portion of the insert, only the elevated portions of the composite coming into contact with the tool holder, clamp, thus reducing the amount of material which must be machined to provide parallelism.